Integrated one-piece rotary mixer and disperser head

Abstract: The mixer and disperser head (1) comprises a cylindrical, tubular mixing chamber (3) having a plurality of equally angularly spaced discharge slots (7) through its periperal wall, a first plurality of impeller blades (11) rigidly connected to one axial end of the mixing chamber (3), a second plurality of impeller blades (27) rigidly connected to the other axial end of the other end of the mixing chamber (3), and a shaft (15) rigidly connected to the first plurality of impeller blades (11) coaxially with and situated quite outside the mixing chamber. The first (11) and second (27) pluralities of impeller blades being mirror-images of each other relatively off-set by an angle of 60° about the rotational axis (5) of the mixer and disperser head (1). The first plurality of impeller blades (11) consists of three identical blades (17) angularly off-set by 120° for each other. Each blade (17) comprising a portion (19) which is leading in the rotational direction (R) of the mixer and dispenser head (1) and a trailing portion (21) forming an inward obtuse angle with the leading portion (19). The leading portion (19) has a first part (23) lying in a plane perpendicular to the axis (5) of rotation and spaced from the one end of the mixing chamber (3) and a second part (24) bent inward about 90° from the first part (23) and rigidly connected such as by welding (9) to the rim of said one end of the mixing chamber (3).

Description: The present invention relates to a rotary mixer and disperser head for operations such as dispersing, dissolving, emulsifying and blending of solids, liquids or gases with other liquids. The mixer and disperser head according to the invention is particularly useful in the food-processing industry, the chemical industry, the pharmaceutical industry and other branches of industry for dispersing and dissolving of solids and semi-solids in liquids. A mixer head for such purposes is shown in Figs. 1 and 2 of US-A-3,170,638. This mixer head has a mixing chamber comprising two sections in the form of truncated cones; one at each end of a cylindrical middle section which is slotted along its periphery, and a central shaft extends through the mixer head. The conical sections act as centrifugal pumps pumping the substances to be mixed into the cylindrical section where in a first stage they undergo a hydraulic shear where the two streams meet. The slots in the middle section act in a second stage as specific shear elements, while a third shear stage occurs when the radial discharge from the head meet the slower moving contents of the mixing vessel. The shear forces act to mix the substances and in particular to disperse and dissolve solids in the fluid mixture. Mixer heads of this type present several disadvantages. Thus, for a given diameter of the mixing chamber and a given rotational speed the throughput is delimited by the smaller cross sectional inlet areas of the conical sections. Further, in acting as centrifugal pumps the conical sections impart to the substances to be mixed a considerable tangential component of velocity which rather than to contribute to the hydraulic shear detracts therefrom. The central shaft extending through the mixing chamber reduces the volume thereof and thereby the retention time therein for the fluid mixture. Finally are such mixer heads not immediately accessible for ocular inspection after a cleaning-in-place procedure (CIP-procedure) due to the presence of the conical sections and the throughgoing shaft. A mixer and disperser head is furthermore shown in Figs. 1-3 of US-A-4,900,159. In this mixer head a pair of impellers are clamped to each end of a generally cylindrical mixing chamber by means of a shoulder and a nut on a shaft extending through a bore in a central hub in the mixing chamber. The mixing chamber has a plurality of axially extending slots in its peripheral wall which is connected to the central hub by means of a radial flange placed in the middle of the mixing chamber and as a partition separating that in two chambers. Also in this mixer head the central hub and the flange reduce the volume of the mixing chambers and thereby the retention time therein for the fluid mixture, and the same parts will likewise impart a rotational velocity to the substances to be mixed, i.e. a tangential component of velocity, which will detract from the shear imparted to the fluid mixture when discharged through the elongate slots. The flange or partition prevents that the two streams from the opposite ends of the mixing head meet and thereby undergo a hydraulic shear. This known mixer head is completely unsuited for a CIP-procedure partly because of the many unaccessible corners therein where particulate matter or substances with high viscosity or adhesiveness may accumulate and partly because of the impellers clamped flatly on to the ends of the cylindrical mixing chamber making an ocular inspection of the inner of the mixing head practically impossible. In fact, a thorough cleaning of this known mixer and disperser head necessitates a complete disassembling of the head, separate cleaning of each of its parts, and reassembling again thereof. It is now the object of the present invention to provide a rotary mixer and disperser head which will avoid the aforesaid drawbacks and where the volume of the mixing chamber is not reduced by an axially extending shaft or hub and flange so that the mixing chamber presents the greatest possible volume relative to its outer dimensions, where the circular motion imparted to the substances to be mixed in the mixing chamber is kept as low as possible and the mechanical shear imparted thereto by the axially extending slots thereby kept as high as possible, where a high liquid shear in the substances is obtained in the mixing chamber when the two counter-directed in-flow streams meet therein having high axial velocities and a rotary mixer and disperser head which is particularly well-suited for the CIP-procedure and is easily inspected ocularly after such procedure. Furthermore, the mixer and disperser head according to the invention should be manufactured as a high-quality integral one-piece product by simple and inexpensive technological methods. According to the invention this is obtained by a rotary mixer and disperser head comprising: a shaft adapted to be connected to a rotatable drive shaft, a mixing chamber coaxial with and rigidly connected to said shaft, said mixing chamber being of generally cylindrical shape and having through its peripheral wall a plurality of discharge openings, particularly equally angularly spaced elongated slots extending in a generally axial direction of the chamber, a first plurality of equally angularly spaced impeller blades at one axial end of said mixing chamber, each of said first plurality of impeller blades having a leading edge disposed axially outside of said one axial end, and a trailing edge disposed axially inward from said leading edge to the mixing chamber, and a second plurality of equally angularly spaced impeller blades at the other axial end of said mixing chamber, each of said second plurality of impeller blades having a leading edge disposed axially outside of said other axial end, and a trailing edge disposed axially inward from said leading edge to the mixing chamber, in which each of said first plurality of impeller blades comprises a leading portion having a first part extending in a plane substantially perpendicular to the axis of the mixing chamber, the radially inner end of the first part being rigidly connected to said shaft which is situated completely outside the mixing chamber, and a second part bent about 90° inward from said first part to the mixing chamber and having its free end spaced from said plane rigidly connected to said one axial end of the mixing chamber, and a trailing portion integral with and forming an obtuse angle with the first part of said leading portion and in a plane projection having the shape of a sector of an annulus, and in which each of said second plurality of impeller blades comprises a leading portion having a first part positioned outside the mixing chamber and extending in a plane substantially perpendicular to the axis of the mixing chamber, the radially inner end of the first part being joined to the similar inner ends of the other impeller blades of said second plurality of impeller blades, and a second part bent about 90° inward from said first part to the mixing chamber and having its free end spaced from said plane rigidly connected to said other axial end of the mixing chamber, and a trailing portion integral with and forming an obtuse angle with the first part of said leading portion and in a plane projection having the shape of a sector of an annulus, each of the trailing portions of the first and the second pluralities of impeller blades being directed from the leading portion into the mixing chamber and positioned behind the leading portion in the rotation direction of the mixer. By this construction of the mixer and disperser head the shaft is disposed entirely outside the mixing chamber and only rigidly connected to the radially inner ends of the first plurality of impeller blades. Due to the absence of the shaft from the mixing chamber this has a maximum volume providing for an optimum retention time for the fluid medium therein and the shaft can of course not impart any rotational movement to that medium. The particular design of the impeller blades impart to the in-flow from each end of the mixing chamber an inwardly directed thrust and a high velocity having a pre-dominating axial component thereby creating an intense hydraulic shear in the fluid mixture while at the same time imparting a high mechanical shear thereto. This particular design also allows for an ocular inspection of the inner parts of the mixer and disperser head, and the integral one-piece construction thereof leaves no corners wherein polluting matter may accumulate so that the inventive mixer and disperser head is well-suited for a CIP-procedure. The different parts of the mixer and disperser head may readily be manufactured from stock materials such as tubing and sheet materials by simple technological processes such as turning, milling, punching and stamping and assembled by joining processes such as welding or adhesive bonding. In a preferred embodiment of the mixer and disperser head according to the invention at least some of said first and second pluralities of impeller blades have formations for creating turbulence or shear in a fluid mixture passing thereover. This further adds to the shear forces mechanically imparted to the fluid mixture by the impeller blades. The said formations may preferably be indentations at the trailing edges of said impeller blades, and said indentations have more preferably a generally castellation-like profile. As another preferred feature the trailing edge of each of said plurality of elongated slots through the peripheral wall of said mixing chamber forms an acute angle with the tangent to the inside of said wall at the point of intersection. This feature adds further to the shear forces introduced in the fluid mixture as it leaves the inventive mixer and disperser head. It is preferred that the various parts of the mixer and disperser head of the invention are made from a metallic material such as stainless steel and rigidly connected to each other by means of welding so as to form an integral one-piece unit. A preferred embodiment of the rotary mixer and disperser head according to the invention will in the following be described in more details with reference to the drawings wherein Fig. 1 shows the mixer and disperser head according to the invention in elevation, Fig. 2 shows a plan view of the mixer and disperser head of Fig. 1 as seen from above, Fig. 3 shows a plan view of the mixer and disperser head of Figs. 1 and 2 as seen from below, Fig. 4 shows a broken cross sectional view along the line IV-IV in Fig. 2, Fig. 5 shows a broken cross sectional view along the line V-V in Fig. 2, and Fig. 6 shows in a somewhat greater scale a broken cross-sectional view generally along the line VI-VI in Fig. 1 through one of the elongated slots in the peripheral walls of the mixing chamber. In Figs. 1, 2 and 3, 1 generally indicates a rotary mixer and disperser head according to the invention. The mixer and disperser head 1 comprises a tubular mixing chamber 3 preferably made of stainless steel and having a circular cross section and a central axis 5. Spaced equally angularly are through the wall of mixing chamber 3 in the axially middle region thereof provided a plurality of axially extending elongated discharge slots 7. Connected to the upper planar rim of mixing chamber 3 by weldings such as at 9 is a first set of impeller blades preferably made of stainless steel and generally indicated as 11, and connected to the first set of impeller blades 11 by welding such as at 13 is a shaft 15 also preferably of stainless steel and situated above the first set of impeller blades 11 and coaxial with the mixing chamber 3. The first set of impeller blades 11 comprises three identical impeller blades 17 (see Fig. 2) disposed angularly offset by 120° for each other around the central axis 5. Each of the impeller blades 17 comprises a leading portion 19 (leading in the direction of rotation "R" of the mixer and disperser head 1) and a trailing portion 21. As best seen in Figs. 4 and 5 the leading portion 19 of each of the impeller blades 17 has a first part 23 extending in a plane perpendicular to the axis 5, and a second part 24 bent inward about 90° from the first part 23 and connected by welding such as at 9 to the upper rim of the mixing chamber 3. The radially inner end of the first part 23 is connected to the shaft 15 by means of welding such as at 13. The trailing portion 21 forms as best seen in Fig. 4 an obtuse inward angle with the first part 23 of the leading portion 19 and has in a plane projection the shape of a sector of an annulus. Its trailing edge has indentations with a castellation-like profile 25. Connected to the lower planar rim of mixing chamber 3 is a second set of impeller blades preferably made of stainless steel and generally indicated as 27. The second set of impeller blades 27 is a mirror image of the first set of impeller blades 11 and is offset relative thereto by 60° in the direction "R" of rotation of the mixer and disperser head 1. This second set of impeller blades 27 will therefore only be described in outlines in the following since more detailed information thereon may be had from the foregoing description of the first set of impeller blades 11 in connection with Figs. 2, 4 and 5. As best seen in Fig. 3 the second set of impeller blades 27 comprises three identical impeller blades 29 angularly offset by 120° for each other about the central axis 5. Each impeller blade 29 comprises a leading portion 31 and a trailing portion 33. The leading portion 31 has a radially inner first part 35 extending in a plane perpendicular to the axis 5 and a radially outer second part 36 bent about 90° inward from the first part 35. The radially inner parts 35 of the three impeller blades 29 are joined in a hub-like central disc 37, and the free ends of the bent parts 36 are connected so as by welding to the lower rim of the mixing chamber 3. The trailing portion 33 of each impeller blade 29 forms an obtuse inward angle with the first part 35 of the leading portion 31 and has in a plane projection the shape of a sector of an annulus. Its trailing edge has indentations with a castellation-like profile 39. From the foregoing description of the first and second sets of impeller blades 11 and 27, respectively, it will easily be understood that they may be made from flat sheet metal by punching using the same set of dies, and by bending such as by stamping trailing portions 21 and bent parts 24 to one side to obtain a set of impeller blades 11 and trailing portions 33 and bent parts 36 to the opposite side to obtain a set of impeller blades 27. As will be seen from Fig. 6, the slots 7 through the peripheral wall of mixing chamber 3 are not made as generally radial extending slots through said wall but are made such as by milling so that the middle plane through slot 7 forms an angle with a radial plane and more particularly so that the trailing edge of slot 7 forms an acute angle with the tangent to the inside surface of the wall at the point of intersection. As explained initially herein this feature contributes to the shear forces introduced into the fluid mixture expelled through slots 7. The trailing edges of slots 7 so formed also enchance the centrifugal pumping action of the mixing chamber 3 by increasing the velocity by which the fluid mixture is expelled from the mixing chamber into the liquid mixture in the surrounding vessel thereby also increasing the hydraulic shear obtained thereby. As shown in Fig. 5 the shaft 15 has a central bore 40 therein provided with an internal thread 41 adapted to be threadingly engaged with a corresponding external thread on a drive shaft (not shown) connected to a drive unit such as an electric motor or a hydraulic or pneumatic motor for rotatably driving the mixer and disperser head 1. Operation of the inventive mixer and disperser head: When thus connected to a drive unit the mixer and disperser head 1 is immersed into the substances to be mixed and/or dispersed contained in a suitable vessel and caused to rotate at high RPM. The first and second sets of impeller blades 11 and 27, respectively, now act as impeller pumps driving the substances from the surrounding vessel in a mainly axial direction into the mixing chamber 3 at a great velocity. Thereby the said substances firstly undergo an abrupt change of relative direction of movement resulting in the introduction of accelerative shear forces therein, secondly the flowing substances are further split up by the castellation-like indentations 25 and 39, respectively, introducing further turbulence and shear therein. Within the mixing chamber 3 the two streams of substances collide substantially axially at high velocities creating a high hydraulic shear. Due to the absence of a high speed rotating shaft or hub and flange there is no rotative force in the central parts of the mixing chamber acting upon the substances. Therefore, the greater part of the substances move toward the periphery in a mainly non-rotative, radial direction whereby - during the expellation of the substances through the discharge slots - the high speed rotating slots act upon the slower moving substances with high mechanical shear. The substances are expelled therefrom with high velocity into the surrounding mixture, whereby they undergo further high hydraulic shear. As compared with the initially mentioned prior art mixer heads this means that shear forces are introduced in the fluid mixtures in at least two further stages of the operation and intensified in the others resulting in an improved over-all performance. Since the visibility of the inner surfaces of the mixer and disperser head according to the invention is only slightly obscured by the presence of the two sets of impeller blades 11 and 27, respectively, the inventive mixer and disperser head lends itself to an ocular inspection after a CIP-procedure. From the foregoing description it will be understood that the various parts of the mixer and disperser head according to the invention may be manufactured at a low cost by simple technological processes and interconnected by welding so as to form an integrated one-piece unit. The discharge openings may have any other appropriate shape than that of axially extending elongated slots, and also the impeller blades may be present in another number than three for each set of impeller blades and may have another shape than that described. Depending on the intended application of the mixer and disperser head it may also be made from other materials than stainless steel, e.g. from plastics materials, or from a combination of plastics materials and metallic materials, and the various parts of the mixer and disperser head may be rigidly connected to each other by other means than welding, e.g. by adhesive bonding.

Claims: A rotary mixer and disperser head (1) comprising: a shaft (15) adapted to be connected to a rotatable drive shaft a mixing chamber (3) coaxial with and rigidly connected to said shaft (15), said mixing chamber (3) being of a generally cylindrical shape and having through its peripheral wall a plurality of discharge openings, particularly equally angularly spaced elongated slots (7) extending in a generally axial direction of said chamber (3), a first plurality (17) of equally angularly spaced impeller blades (11) at one axial end of said mixing chamber (3), each of said first plurality of impeller blades (11) having a leading edge disposed axially outside of said one axial end, and a trailing edge disposed axially inward from said leading edge to the mixing chamber (3), and a second plurality of equally angularly spaced impeller blades (27) at the other axial end of said mixing chamber (3), each of said second plurality of impeller blades (27) having a leading edge disposed axially outside of said other axial end, and a trailing edge disposed axially inward from said leading edge to the mixing chamber (3), in which each of said first plurality (17) of impeller blades (11) comprises a leading portion (19) having a first part (23) extending in a plane substantially perpendicular to the axis (5) of the mixing chamber (3), the radially inner end of the first part (23) being rigidly connected to said shaft (15) which is situated completely outside the mixing chamber (3), and a second part (24) bent about 90° inward from said first part (23) to the mixing chamber (3) and having its free end spaced from said plane rigidly connected (at 9) to said one end of the mixing chamber (3), and a trailing portion (21) integral with and forming an obtuse angle with the first part (23) of said leading portion (19) and in a plane projection having the shape of a sector of an annulus, and in which each of said second plurality of impeller blades (27) comprises a leading portion (31) having a first part (35) positioned outside the mixing chamber (3) and extending in a plane substantially perpendicular to the axis (5) of the mixing chamber (3), the radially inner end of the first part (35) being joined to the similar inner ends of the other impeller blades (29) of said second plurality of impeller blades (27), and a second part (36) bent about 90° inward from said first part (35) to the mixing chamber and having its free end spaced from said plane rigidly connected to said other end of the mixing chamber (3), and a trailing portion (33) integral with and forming an obtuse angle with the first part (35) of said leading portion (31) and in a plane projection having the shape of a sector of an annulus, each of the trailing portions (21,33) of the first (17) and the second (27) pluralities of impeller blades (11) being directed from the leading portion (19,31) into the mixing chamber (3), and being positioned behind the leading portion (19,31) in the rotation direction of the mixer. A mixer and disperser head (1) as claimed in claim 1, characterized in that at least some of said first and second pluralities of impeller blades (17,27) having formations (25,39) for creating turbulence or shear in a fluid mixture passing thereover. A mixer and disperser head as claimed in claim 2, characterized in that said formations are indentations (25, 39) at the trailing end of said impeller blades (11,29). A mixer and disperser head as claimed in claim 3, characterized in that said indentations (25,39) have a generally castellation-like profile. A mixer and disperser head as claimed in claim 1, characterized in that the trailing edge of each of said plurality of elongated slots (7) through the peripheral wall of said mixing chamber (3) forms an acute angle (α) with the tangent to the inside of said wall at the point of intersection. A mixer and disperser head as claimed in claim 1, characterized in that the various parts are made from a metallic material such as stainless steel and rigidly connected to each other by welding so as to form an integral one-piece unit.

Inventors: JENSEN KNUD ERIK JUHL, JORGENSEN POVL JORGEN, JENSEN, KNUD ERIK JUHL, JORGENSEN, POVL JORGEN
Applicants: IN MIX A S, IN-MIX A/S
Application year: 1994
Main classification: B01F15
IPC codes: B01F7, B01F15